Hydrogen sulfide gas is both a contaminant and a pollutant found in natural gas and various industrial gases. In order to prevent emission of hydrogen sulfide gas, which carries the foul odor of rotten eggs and is poisonous, corrosive and flammable, various processes have been developed. Some processes react hydrogen sulfide with sulfur dioxide to yield elemental sulfur (which can be recovered) and water, according to the following reaction:2H2S+SO2→2H2O+3S
The sulfur dioxide can be produced by the combustion of sulfur, suitably including sulfur that is generated in the reaction of hydrogen sulfide with sulfur dioxide. The end result can be a treated natural gas or treated industrial gas emission that is substantially free of both hydrogen sulfide and sulfur dioxide.
U.S. Pat. No. 7,381,393, issued to Lynn, discloses a process for removing hydrogen sulfide (and thus sulfur) from a gas by reaction in a high boiling point organic liquid medium, under heat, with sulfur dioxide. The disclosed process includes the steps of reacting a hydrogen sulfide-containing gas stream with a stoichiometric excess of sulfur dioxide in a reactor to produce a sulfur dioxide-containing gas and liquid sulfur, using an organic liquid medium and a temperature exceeding the melting point of sulfur; withdrawing liquid sulfur from the reactor; withdrawing the sulfur dioxide-containing gas from the reactor; removing the sulfur dioxide from the gas; and recycling the sulfur dioxide for use in the first step of the process.
U.S. Pat. No. 5,928,620, issued to Lynn, discloses an earlier process for removing elemental sulfur from a hydrogen sulfide-containing gas. The process includes the steps of passing the hydrogen sulfide-containing gas through a hydrogen sulfide absorber to obtain a gas having a diminished amount of hydrogen sulfide, stripping the hydrogen sulfide out of the resulting hydrogen sulfide-rich solution to obtain a hydrogen sulfide-rich gas, feeding the hydrogen sulfide-rich gas an sulfur dioxide into a reactor, reacting the hydrogen sulfide and sulfur dioxide to convert about 50% of the hydrogen sulfide to sulfur dioxide and water, combusting the remaining hydrogen sulfide to yield sulfur dioxide, and feeding the sulfur dioxide back into the reactor.
The foregoing processes typically carry out the chemical reaction in a liquid reaction medium using a high boiling organic solvent at a temperature of about 115-150° C. at a pressure that is near or slightly above atmospheric pressure. Examples of suitable organic solvents include diethylene glycol methyl ether (“DGM”), triethylene glycol methyl ether, triethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, and other polyglycol ethers. The use of these solvents contributes significant cost and complexity to the process. Not only are the solvent costs high, but care must be taken to ensure that the solvent vapors are not discharged into the atmosphere and do not leave the reactor with the hydrogen sulfide-depleted gas.